Ubuntu Gnome 14.10 - desktop performance degraded when certain apps are running

If you have Integrated Intel graphics, you could try

sudo apt-get install xserver-xorg-video-intel

then rebooting. This worked for me on a Dell XPS laptop - everything became smooth again. Source: https://bugs.launchpad.net/ubuntu-gnome/+bug/1385764

If you subsequently have problems with

optirun glxgears

giving "Can't open secondary"...

Try,

 sudo apt-get install nvidia-331-updates

then

 gksudo gedit /etc/bumblebee/bumblebee.conf

Under the section [bumblebeed] change the Driver: Driver=nvidia

Under [driver-nvidia] change references in this section from nvidia-current to nvidia-331-updates. That's in the KernelDriver, XorgModulePath and LibraryPath.

Then reboot, and try

optirun glxgears

Source: http://mylinuxexplore.blogspot.co.uk/2014/03/solved-nvidia-cant-access-secondary-gpu.html